1. Field of the Invention
The present invention relates to a device and a method for automatically detecting the termination of a calibration of a geomagnetic sensor. More particularly, the present invention relates to a device and a method capable of detecting the progress of a calibration using slopes of signals outputted from a geomagnetic sensor and the number of slope sign changes, and automatically terminating the calibration.
2. Description of the Related Art
A geomagnetic sensor is a direction search means, and is used in an electronic compass, navigation systems, satellite antenna controls, robot direction controls, game devices, portable terminals, personal digital assistants (PDAs), notebooks, and the like. As alternatives to a geomagnetic sensor, there are speed sensors, gyro sensors, global positioning systems (GPS), and so on, for use as direction search means. In particular, GPS is a world-wide position-determining system using satellites, which has the advantages of no position error accumulation and relatively low price. GPS is used in a wide range of fields, such as in vehicles, vessels, airplanes, construction equipment, notebook computers, and the like. However, GPS has limitations in that it is not able to estimate positions around buildings or in tunnels where electric waves are not received, has a position error of as much as 100 meters, among others. Accordingly, in order to compensate for these limitations, a geomagnetic sensor, an optical fiber gyro, or similar device is used as a sensor for direction measurements, and the GPS and an electronic map are used in combination, to thereby realize high-precision positioning.
A geomagnetic sensor uses a magnetic needle to detect the direction of the magnetic field produced by the Earth, which enables the absolute azimuth to be obtained from the signal X and signal Y that the X-axis coil and Y-axis coil, respectively, of the geomagnetic sensor generate. However, the geomagnetic sensor is easily affected by ambient magnetic fields of buildings, iron bridges, subway trains, and other similar sources, and the output signals of the geomagnetic sensor vary frequently depending upon an assembly state, declined degrees, or measurement environments of the sensor. Accordingly, the geomagnetic sensor must be calibrated to obtain precise orientation measurements.
FIG. 1 shows a conventional calibration process for a geomagnetic sensor. In a calibration process for a geomagnetic sensor, after the sensor is turned once or twice, the process measures output signals X and Y, and calculates calibration factors of offset and scale using a calibration algorithm. In subsequent measurements, the calibration factors are used for calibration so that the signals of the geomagnetic sensor become precise direction change values.
The conventional calibration process detects a calibration termination state based on a user's intuition or the detection of whether maximum values are repeated.
First, use of the user's intuition is a method in which the user turns a geomagnetic sensor once or twice. This method does not provide an easy calibration process since the user does not know the progress of the calibration process, i.e., the calibration progress state, which often leads to the calibration process not being properly performed.
The method of detecting whether the maximum values are repeated detects the progress of the calibration process, i.e., the calibration progress state, using the number of times repeated maximum and minimum values of signals are output from a geomagnetic sensor. This method relies on the fact that the maximum and minimum values for calculating the calibration state are directly associated with calibration factors. Accordingly, since the maximum and minimum values change depending upon calibration environments and the errors of the calibration factors are induced when the changing values are used in monitoring the calibration process, situations occur when the sensor is not able to detect precise calibration factors nor calculate the termination of the calibration process, i.e., the calibration termination state.